Radio, the transmission of modulated electromagnetic waves, has been used as a method of communication since the late 19th century. Several different techniques are utilized to modulate radio signals including (but not limited to) modulation techniques that utilize variations in the amplitude, frequency, and/or phase of a radio frequency or RF signal to communicate analog or digital data.
Radio is ideal for use as a communication method to provide remote control and communication with persons and machinery in the field. For example, radio communication may be utilized to implement a positive train control system. A positive train control system allows for location monitoring and speed tracking of trains and allows an operator to take control of a train in the event that the train engineer experiences difficulties. In 2008, a freight train collided with a commuter train in the Chatsworth district of Los Angeles, Calif. due to a distracted train engineer on the commuter train running a red light and colliding into the freight train, which had been given the right of way by the train dispatcher. A positive train control device is designed to enable a train dispatcher to remotely intervene and prevent collisions.
In many regions, cellular data networks have been established that enable data to be transmitted and received using mobile devices equipped with an appropriately configured data radio. Several standards exist for cellular data, including General Packet Radio Service (GPRS), Enhanced Data rates for GSM Evolution (EDGE), Evolved High-speed Packet Access (HSPA+), Evolution-Data Optimized (EVDO), Worldwide Interoperability for Microwave Access (WiMAX), and 3GPP Long Term Evolution (LTE).